1. Field of the Invention
The present invention relates to an information recording apparatus for producing a master medium of an information recording medium for replicas such as optical disks (i.e., compact disks, laser disks and the like).
2. Description of the Prior Art
The conventional art relate to the production of a conventional master disk for producing the information recording medium. Through a lens barrel of a scanning electron microscope, an electron beam directly irradiates a principal surface of a master disk while the disk rotates. At the same time, the master disk is moved in a direction parallel to its principal surface so that a spiral pattern of the thus irradiated spots (i.e., recorded pits) is formed on the surface of the master disk.
Now, the lens barrel 1 for irradiating the electron beam will be described in construction with reference to FIG. 1. As shown in FIG. 1, electrons emitted from a filament 1a energized with a high voltage of approximately 10 kV pass through a Wehnelt electrode 1b and an anode 1c to become an electron beam. The beam then passes through a first electromagnetic lens 1d and a second electromagnetic lens 1e while the beam is converged therethrough. The thus converged beam reaches a deflection electrode if through which the electron beam is focused on a target (i.e., master disk 2).
Incidentally, by applying a predetermined voltage to the deflection electrode (which is denoted by the reference character "1f"), it is possible to adjust the electron beam in position and in operation, for example such as in scanning.
Further, a drive unit for carrying and driving the master disk 2 will be described with reference to FIG. 2. As shown in FIG. 2, in the drive unit, a base 6 is provided with a pair of projecting support rails 6a on which a traveling stage 5 is slidably mounted. Supported on the traveling stage 5 is a spindle motor 4a of a hydraulic bearing type. Fixedly mounted on an upper end of a spindle of the motor 4a is a turn table 4 which is rotatably driven with torque supplied from a drive source. The drive source is constructed of an oil jet 3a ejected at high speed from an oil nozzle 3 which is also supported on the traveling stage 5. The oil jet 3a is tangentially directed against an outer peripheral surface of the turn table 4 to hit the same in the surface so that the turn table 4 is rotatably driven by the oil jet 3a.
On the other hand, threadably connected with a lower portion of the traveling stage 5 is a screw member 8 which is rotatably driven by a drive motor 7 to have the traveling stage 5 and the master disk 2 thereon moved along the support rails 6a.
By the above combination of necessary components such as the lens barrel and the drive unit comprising the turn table and the like, it is possible to record information on the master disk. In this case, since it is not desirable to transmit the electron beam through media other than a vacuum, these components are contained in a vacuum chamber to operate therein.
However, the conventional information recording apparatus having the above construction suffers from the following problems. As described above, since the system employs the oil jet as a means for producing torque, there is a fear that the vacuum chamber has its interior contaminated with oils, the oils being evaporated and adhering to the lens barrel of the electron microscope so as to impair its function.
As for the turn table, its torque produced by the use of the oil jet largely depends on the oil's properties such as its jet velocity, temperature, viscosity and the like. Further, a predetermined time lag is involved before the turn table (which has its outer peripheral surface subjected to the oil jet to receive the torque) reaches a predetermined rotational speed. In addition, such predetermined time lag is involved also when the turn table stops its rotational operation after the oil jet stops. Due to the presence of above-mentioned disadvantages, the system employing the oil jet is poor in responsivity and in controllability, and, therefore is not desirable to drive the master disk.